PRE-COORDINATE INDEXING MODELS 

You will recall from your study of the sub-section 14.5.2 of Unit 14 that the pre-coordinate index constitutes a collection of index entries in which concepts from documents are co-ordinated according to a  plan using a linear  sequence at the time the index headings are prepared. These  concepts  are then represented  either by symbols (when using a scheme of classification) or words of the indexing language in use. The next step is to synthesize or to put the components in an order recommended by  the rules of the language. This means that the concepts  are pre-coordinated and the index  file  consisting of a collection of such pre-coordinated concepts that are available  in the library's  collection of documents. Those pre-coordinated indexes when arranged alphabetically are known as alphabetical subject indexes or alphabetical subject  catalogues. When arranged  according to a scheme of  classification they are known as classified indexes or classified catalogues. 

All pre-coordinate indexing models are based on classificatory principles such as, facet analysis and  synthesis. The functions performed by  a pre-coordinate indexing models are discussed below: 

1. Collocating Function: The function is to bring together in the file document surrogates on the same similar subjects. Most subjects to be dealt with would be multi-conceptual (e.g., Survey of bank credits to industrial estates). Rules are necessary for the ordering of terms in an index headings, so that indexers represent the same' or similar subjects consistently, thereby helping the indexer to perform the  collocating function effectively.
2. Retrieval Function:  The function is to recall references to documents in response to generic and specific enquiries. This is aided by providing entries under each significant term as well as reference entries 'see' and 'see also' in the index. The reference entries help in bringing together narrower and related subjects together. Another way of aiding the retrieval function is to subject each enquiry  to conceptual analysis and translation before the index is searched. Once the search  strategy is formulated and the index is ready to be searched, the actual retrieval  itself is aided by the proper collocation of entries in the index. 
3. In a pre-coordinate index  each significant term in a string becomes the lead term or filing element. Associated with the need to provide multiple entries is also the need to see that each of these entries is intelligible and unambiguous in covering the intended meaning. 
4. It should support searches with varying precision and recall requirements. 
5. It enables the searcher to interact with the system in obtaining satisfactory results. 
6. It is necessary to establish syntactical relationships between the terms of a  subject statement in retrieval file. This relationship connects the  components of a subject statement into a coherent whole and so determine its overall meaning. 
7. It is necessary to have semantic relationships between the terms of a subject statement in a retrieval file. This relationship exists between a specific concept and the family of inter-connected ideas with which it is generally associated. These two relationships are important for retrieval file to enable generic as well as specific searches.